1. Field of the Invention
The present invention relates to a communication apparatus and method, and functional module, and specifically relates to a communication apparatus and method, and functional module whereby improvement in design flexibility, suppression of increase in manufacturing costs, and elimination of multipath influence with wireless communication can be realized.
2. Description of the Related Art
There has been a problem wherein when high-speed high-volume communication, of which communication of video signals is representative, is performed in a constant multipath environment, generally-performed decoding results in loss in signals due to DC offset or the like caused by multipath, which prevents communication from being performed. The constant multipath mentioned here is caused with an environment wherein a transmitter and receiver which perform wireless communication are covered with metal, and examples of such an environment include a case wherein wireless communication is performed within an electronic device.
For example, description will be made how a constant multipath signal changes in a case wherein wireless communication employing ASK (Amplitude Shift Keying) modulation is performed within the casing of an electronic device.
White noise (e.g., thermal noise) or colored noise (e.g., noise emitted from another LSI) which is included in the casing, or a signal reflected or diffracted at the wall face or board within the casing is added to radio waves emitted within the casing, and when receiving such radio waves, the original transmitted signal waveform is not reproduced, rather, a distorted waveform is reproduced instead. In particular, a serious problem is caused by deterioration due to reflected waves input to a reception point with the same magnitude as the power of the transmitted signal.
The reflected waves can be regarded as a signal having the same signal waveform as the signal waveform to be received, but having a different route (accordingly, time for transmission is shifted). When such reflected waves are overlapped with the original signal at a reception point, the waveform of the original signal is distorted, interference is caused, and consequently decoding becomes difficult.
Thus, signal waves made up of transmitted waves (original signal), and reflected waves transmitted with a different route from that of the transmitted waves being overlapped, are also referred to as multipath waves, and influence due to multipath waves becomes a serious problem as the speed of a transmission signal increases. Also, with the related art, deterioration in a reception waveform due to multipath caused within the casing of an electronic device, or the like is generally constant over time, and time over which there is influence due to multipath waves is short with a reception waveform, and accordingly, an environment such as within the casing of an electronic device can be understood as being a constant multipath environment.
With such a constant multipath environment, there are the following methods as a method for attempting to improve communication quality.
For example, there can be conceived a method wherein OFDM (Orthogonal Frequency Division Multiplexing) is employed at the time of modulation/demodulation, thereby realizing improvement in communication quality. However, when employing OFDM, fast Fourier transform often has to be performed, and consequently, increase in power consumption causes a problem.
Also, for example, there can be conceived a method wherein SS (Spread Spectrum) and rake reception are employed, thereby realizing improvement in communication quality. However, when employing SS, signal processing of which the speed is higher than a transmission signal has to be performed, and accordingly, this is unsuitable for broadband communication such as transmission of video signals.
Also, for example, there can be conceived a method wherein a multi-antenna is employed, thereby realizing improvement in communication quality. However, in order to obtain the advantage of the multi-antenna, the spacing between the antennas has to be sufficiently separated, and accordingly, for example, in a case wherein a multi-antenna is realized on a board within the casing of an electronic device, placement is restricted, leading to increase in the size of the device, and restriction of design flexibility.
Further, there can be conceived a method wherein a wave absorber is employed, thereby realizing improvement in communication quality (e.g., see Japanese Unexamined Patent Application Publication No. 2004-220264). According to the technique of Japanese Unexamined Patent Application Publication No. 2004-220264, there is provided a wave absorber within the casing, which absorbs electromagnetic waves with a frequency band of extremely-short pulses, and prevents the reflection thereof. This wave absorber is configured of ferrite, urethane, or the like having high absorption characteristics as to a frequency band of extremely-short pulses as a material, and is installed by a plate-shaped wave absorber being adhered to the inner wall of the casing as appropriate, for example.